Mineral phase
IMA name
Chamosite
Type
Class
silicate mineral
Compound type
phyllosilicate
Chemical composition
Formula
$(Mg,Fe^{2+},Fe^{3+})_5Al(Si_3Al)O_{10}(OH,O)_8$
Chemical formula
(Mg,Fe2+,Fe3+)5Al(Si3Al)O10(OH,O)8
Elemental formula
(Mg)0-2 (Fe2+)2-4 (Fe3+)0-1 Al2 Si3 O18 (H)6-8
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Mg$ Magnesium element 0 - 2 constituent element main
$Fe^{2+}$ Iron(II) cation element 2 - 4 constituent element main
$Fe^{3+}$ Iron(III) cation element 0 - 1 constituent element main
$Al$ Aluminium element 2 constituent element main
$Si$ Silicon element 3 constituent element main
$O$ Oxygen element 18 constituent element main
$H$ Hydrogen element 6 - 8 constituent element main
Composition comments
Fe3+ is minor or nonexistent. Common impurities: Ca, Na
Chemical functions
  Function Number
$(OH)^-$
Chemical bonds
  Bond Number
$O^--H$ 1
Oxides
Formula $MgO$ $Al_{2}O_{3}$ $FeO$ $Fe_{2}O_{3}$ $SiO_{2}$ $H_{2}O$
Mass fraction (%)

Strunz

Class
silicates (09)
Division
phyllosilicate (09.E)
Family
with mica sheets, composed of tetrahedral and octahedral nets (09.EC)
Code
09.EC.55

Dana

Major class
silicates (VIII)
Class
phyllosilicate sheets of six-membered rings (71)
Type
interlayered 1:1, 2:1, and octahedra (71.04)
Group
Chlorite group (Tri-Dioctahedral) (71.04.01)
Code
71.04.01.07
Phase type
crystalline
Crystal system
monoclinic
Crystal class
prismatic
Crystal class symbol
2/m (C2h)
Crystal spacegroup
C2/m
Molar mass
664.18 $g/mol$
Density
3 - 3.4 $g/cm^3$
State NTP
solid
Refringence type
biaxial
Refringence sign
negative
Birefringence
0.0700
Refraction index $n_{\alpha}$
1.595 - 1.671
Refraction index $n_{\beta}$
1.599 - 1.684
Refraction index $n_{\gamma}$
1.599 - 1.685
Dispersion V
r < v weak
Pure color
green
Color
Green, Gray, Greenish gray, Brown, Blackish green, black
Diaphaneity
translucent to opaque
Luster
vitreous
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